Spray guns for applying plural component materials such as fast set foams are well known and typically available in both mechanical purge and air purge variants. The previously known means of purging two component material in mechanical purge guns was through a mechanical purge rod sliding through the mixing bore. This arrangement has the issue of the purge rod sticking inside the bore due to buildup of the sprayed material.
In air purge guns, the previous means of purging two component material was through a high pressure air purging (blast of air through mixing chamber). This design lead to buildup on the internal passages of the mixing chamber and spray tip causing the spray pattern to deteriorate, requiring the operator to clean the mixing chamber to restore functionality.